Flies are implicated as vectors of various organisms causing both chronic and acute mastitis in cattle.
Summer mastitis, due to Corynebacterium pyogenes, is mainly spread by the head fly Hydrotaea irritans and the face fly Musca autumnalis (Hillerton, 1985).
Flies are also involved in the spreading and transmission of other forms of mastitis, due to other species of Corynebacterium, staphylococcal and possibly streptococcal infections (Braverman, 1999, Yeruham, 1996).
Heifers from herds using fly control usually have a lower prevalence of mastitis than herds without fly control (Nickerson, 1995).
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